Hierarchically nanostructured Ni(OH)2–MnO2@C ternary composites derived from Ni-MOFs grown on nickel foam as high-performance integrated electrodes for hybrid supercapacitors

Abstract

Metal-organic frameworks (MOFs) have been widely used as templates for many nanomaterials and are considered to be a promising electrochemical energy storage material. However, while taking advantage of the unique porous structures of MOFs or MOFs’ derivatives, it is still a big challenge to have their conductivity improved to a large extent. Herein, a facile strategy is employed to prepare a hierarchical Ni-MOF-derived ternary composite, which is composed of nanosheet Ni(OH)2, MnO2 and graphite carbon. The Ni-MOF in-situ grown on nickel foam (NF) were used as template to prepare the Ni(OH)2-MnO2@C ternary composite, so that the self-supporting binder-free Ni(OH)2-MnO2@C/NF integrated electrode was resulted. The Ni(OH)2–MnO2@C composite had a hierarchical nanosheet structure. The as-prepared Ni(OH)2–MnO2@C/NF was found to exhibit a high specific capacity of 2.9C cm−2 (965.1C g−1) at a current density of 2 mA cm−2 and excellent cycle stability (capacity retention of 93.9% after 5000 cycles). Furthermore, the as-assembled Ni(OH)2–MnO2@C//activated carbon hybrid supercapacitor exhibited a high specific energy density of 39.1 Wh kg−1 with a power density of 221.4 W kg−1. One contribution for the superior electrochemical performance of the Ni(OH)2–MnO2@C composite is from its hierarchical nanostructure, which not only has a large specific surface area, but also provides efficient electron and ion transport channels as well as rich redox sites. Another contribution is from its excellent electrical conductivity as a result of the presence of graphitic carbon and the absence of non-conductive binder in the composite electrode as well as the direct contact between the electrode and current collector. This work provides an effective approach for fabricating high-performance composite electrodes from MOFs.